Call Combinatoriality in Birds

The structural diversity of vocal communication systems across birds not only reflects considerable variation in repertoire size, but also in the organisation of acoustic elements, both within and across calls. A fundamental challenge for understanding this variation lies in the subjective nature of call repertoire classification, where inconsistent methodological frameworks risk confounding comparative analyses of vocal complexity. Whether element sharing across functionally distinct vocalisations is associated with larger element inventories and more diverse call repertoires, and whether such relationships reflect efficient coding under production and perceptual constraints, remains largely untested at the comparative level. This thesis addresses both challenges across two complementary studies. First, using the white-browed babbler (Pomatostomus superciliosus) as the focal species, I develop a standardised, bottom-up approach to call repertoire classification, using temporal distributions of inter-element intervals to objectively define call boundaries and compile a comprehensive vocal repertoire. This method identifies a minimum of 19 discrete vocal elements sustaining at least 27 distinct calls, with evidence for a predominantly syntax-like combinatorial system where many elements retain independent meaning prior to recombination across multiple hierarchical levels. Second, I examine the relationship between element sharing, element inventory size, and call repertoire size across 95 avian species using phylogenetic generalised least squares and evolutionary transition modelling. Recombinatoriality emerged as a significant positive predictor of repertoire size, with recombinatorial species achieving 66-68% more calls than both non-sharing groups. Contrary to efficiency-based predictions, recombinatorial species possessed more element types rather than fewer, with repertoire expansion appearing to follow, rather than precede, the evolution of sharing. Evolutionary transitions were consistently stepwise, identifying a selectively stable non-recombinatorial intermediate absent from existing theoretical frameworks, suggesting the initial transition to multi-element calls is driven by perceptual rather than productive pressures. Together, these findings support recombinatoriality as a generative property of avian vocal repertoires, offering a comparative framework for understanding the evolutionary origins of combinatorial communication, including the origins of human language.<p></p>

Author dc:creator

• Alexander Chapman (8450826)

• combinatorial communication

Statement dc:rights

• All rights reserved

Identifier

10779/exe.33016919.v1

OAI identifier oai:identifier

oai:figshare.com:article/33016919